1. Field of the Invention
Embodiments of the present invention relate generally to micro-electro-mechanical and nano-electro-mechanical systems and more specifically to such systems having one or more microfluidic lubricant channels.
2. Description of the Related Art
As is well known, atomic level and microscopic level forces between device components become far more critical as devices become smaller. Problems related to these types of forces are quite prevalent with micromechanical devices, such as micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS). In particular, “stiction” forces created between moving parts that come into contact with one another, either intentionally or accidentally, during operation are a common problem with micromechanical devices. Stiction-type failures occur when the interfacial attraction forces created between moving parts that come into contact with one another exceed restoring forces. As a result, the surfaces of these parts either permanently or temporarily adhere to each other, causing device failure or malfunction. Stiction forces are complex surface phenomena that generally include capillary forces, Van der Waal's forces and electrostatic attraction forces. As used herein, the term “contact” refers generally to any interaction between two surfaces and is not limited to the actual physical touching of the surfaces. Some examples of typical micromechanical devices are RF switches, optical modulators, microgears, accelerometers, worm gears, transducers, fluid nozzles, gyroscopes, and other similar devices or actuators. It should be noted that the term “MEMS device” is used hereafter to generally describe a micromechanical device, and to cover both MEMS and NEMS devices discussed above.
Stiction is especially problematic in devices such as the RF switch, optical modulator, microgears, and other actuators. Various elements in these devices often interact with each other during operation at frequencies between a few hertz (Hz) and a few gigahertz (GHz). Various analyses have shown that, without adding some form of lubrication to these types of devices to reduce stiction and wear between component surfaces, product lifetimes may range from only a few contacts to a few thousand contacts, which is generally well below a commercially viable lifetime. Consequently, one of the biggest challenges facing the MEMS and NEMS industries is the long-term reliability of contacting microstructures in the face of stiction.
Several techniques to address stiction between two contacting surfaces have been discussed in various publications. One such technique is to texture the contact surfaces (e.g., via micro patterning or laser patterning) to reduce the overall adhesion force by reducing the effective contact area. Another such technique involves selecting specific materials from which the contacting surfaces are made to lower the surface energy, reduce charging, or contact potential difference between components.
Moreover, some prior references have suggested the insertion of a lubricant into the region around the interacting devices to reduce the chance of stiction-related failures. Such a lubricant often times is in a solid or liquid state, depending on the properties of the material, and the temperature and pressure or environment in which the lubricant is placed. In general, the terms a “solid” lubricant or a “liquid” lubricant is a lubricant that is in a solid or liquid state under ambient conditions, i.e., room temperature and atmospheric pressure. Some prior art references describe a lubricant as being in a “vapor” state. These references use the term vapor phase lubricant to generally describe a mixture of components that contain a carrier gas (e.g., nitrogen) and a vaporized second component that is a solid or liquid at temperatures and pressures near ambient conditions (e.g., STP). In most conventional applications, the solid or liquid lubricant remains in a solid or liquid state at temperatures much higher than room temperature and pressures much lower than atmospheric pressure conditions.
Examples of typical lubricants that are solid or liquid at ambient conditions and temperatures well above ambient temperature can be found in references such as U.S. Pat. No. 6,930,367. Such prior art lubricants include dichlorodimethylsilane (“DDMS”), octadecyltrichlorosilane (“OTS”), perfluoroctyltrichlorsilane (“PFOTCS”), perfluorodecanoic acid (“PFDA”), perfluorodecyl-trichlorosilane (“FDTS”), perfluoro polyether (“PFPE”) and/or fluoroalkylsilane (“FOTS”), that are deposited on various interacting components by use of a vapor deposition process, such as atmospheric chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), or other similar deposition processes.
The technique of forming the low-surface energy organic passivation layer on the surface of a MEMS component is commonly referred to in the art as “vapor lubricant” coating. One serious draw back to using a low-surface energy organic passivation layer, such as self-assembled monolayer (SAM) coatings, is that they typically are on the order of one monolayer thick. Generally, these types of coatings have a very limited usable lifetime, since they are easily damaged or displaced due to impact or wear created by the interaction of the various moving components. This inevitably happens in MEMS devices with contacting surfaces that are subject to frequent contact in use and a large number of contacts during the product lifetime, such as in light modulators and RF switches. Without some way to reliably restore or repair the damaged coatings, stiction occurs, and device failure results.
As shown in FIG. 1A, one approach for lubricating MEMS components is to provide a getter 110 within the package 100 (that includes a base 111, a lid 104, and a seal 106) in which an array of MEMS devices 108 resides. FIG. 1B illustrates one conventional package 120 that contains a MEMS device 108 and a getter 110 positioned within the head space 124 of the package 120. The package 120 also contains a package substrate 128, window 126 and spacer ring 125. These two configurations are further described in U.S. Pat. No. 6,843,936 and U.S. Pat. No. 6,979,893, respectively. These conventional devices employ some type of reversibly-absorbing getter to store the lubricant molecules in zeolite crystals or the internal volume of a micro-tube. In these designs, a supply of lubricant is maintained in the getter 110, and an amount of lubricant needed to lubricate the MEMS device 108 is discharged during normal operation. However, adding the reversibly absorbing getter, or reservoirs, to retain the liquid lubricants increases package size and packaging complexity and adds steps to the fabrication process, all of which increase piece-part cost as well as the overall manufacturing cost of MEMS or NEMS devices. Thus, forming a device that uses these techniques generally requires a number of labor-intensive and costly processing steps, such as mixing the getter material, applying the getter material to the device-containing package, curing the getter material, conditioning or activating the getter material, and then sealing the MEMS device and the getter within the sealed package.
Particles, moisture, and other contaminants found in our everyday atmospheric environment deleteriously effect device yield of a MEMS fabrication process and the average lifetime of a MEMS device. In an effort to prevent contamination during fabrication, the multiple process steps used to form a MEMS device are usually completed in an ultra-high grade clean room environment, e.g., class 10 or better. Due to the high cost required to produce and maintain a class 10 or better clean room environment, the more MEMS device fabrication steps that require such a clean room environment, the more expensive the MEMS device is to make. Therefore, there is a need to create a MEMS device fabrication process that reduces the number of processing steps that require an ultra-high grade clean room environment.
As noted above, in an effort to isolate the MEMS components from the everyday atmospheric environment, MEMS device manufacturers typically enclose the MEMS device within a device package so that a sealed environment is formed around the MEMS device. Conventional device packaging processes commonly require the lubricating materials that are contained within the MEMS device package be exposed to high temperatures during the MEMS device package sealing processes, particularly wafer level hermetic packaging. Typically, conventional sealing processes, such as glass frit bonding or eutectic bonding, require that the MEMS device, lubricants, and other device components are heated to temperatures between about 250° C. to 450° C. These high-bonding temperatures severely limit the type of lubricants that can be used in a device package and also cause the lubricant to evaporate away or break down after a prolonged period of exposure. In addition, lubricant that has evaporated during high temperature bonding processes can later re-condense onto and contaminate sealing surfaces. Therefore, there is also a need for a MEMS device package-fabricating process that eliminates or minimizes the exposure of lubricants to high temperatures during the device fabrication process.